High pressure pump

ABSTRACT

A gas chamber is placed adjacent to a variable volume chamber of a high pressure pump. The gas chamber includes an inner blocking wall, which borders on the variable volume chamber and contacts fuel in the variable volume chamber, an outer blocking wall, which is opposed to the inner blocking wall, and gas, which fills a space that is defined between the inner blocking wall and the outer blocking wall.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2011-15643 filed on Jan. 27, 2011.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a high pressure pump.

2. Description of Related Art

A high pressure pump, which supplies fuel to a fuel supply system of an internal combustion engine, is known. Fuel, which is drawn out of a fuel tank, is drawn into a pressurizing chamber upon downward movement of a plunger in a cylinder hole of the high pressure pump and is metered upon upward movement of the plunger in the cylinder hole.

Furthermore, it is known to provide a mechanism, which reduces pressure pulsation of low pressure fuel, in the previously known high pressure pump.

For instance, in a high pressure pump recited in DE102004063075A1, a damper chamber (pressure dumper) and a variable volume chamber (compensation chamber) are provided as a fuel pressure pulsation reducing mechanism.

However, in the high pressure pump of DE102004063075A1, the variable volume chamber (the compensation chamber) is covered by only a portion (sleeve part) of a seal element (stop element). Therefore, the fuel in the variable volume chamber may be heated by heat, which is conducted from a heated engine head located adjacent to a cam that reciprocates a plunger. Also, the fuel in the variable volume chamber may be heated by lubricating oil (including engine oil), which is initially applied to the cam or therearound and is dispersed over the seal element. When the fuel in the variable volume chamber is heated to the high temperature in this way, the fuel may possibly be vaporized. When the fuel in the variable volume chamber is vaporized, the high pressure pump may have a difficulty of drawing fuel, so that the operational malfunction of the high pressure pump may occur.

SUMMARY OF THE INVENTION

The present invention addresses the above disadvantages.

According to the present invention, there is provided a high pressure pump, which includes a plunger, a pump body, variable volume chamber forming means and a gas chamber. The pump body includes a cylinder hole, a pressurizing chamber, a low pressure fuel passage and a discharge passage. The plunger is adapted to reciprocate in an axial direction thereof in the cylinder hole. The pressurizing chamber is communicated with the cylinder hole, and fuel is pressurized in the pressurizing chamber by reciprocating movement of the plunger. The low pressure fuel passage communicates between the pressurizing chamber and a fuel inlet. The discharge passage communicates between the pressurizing chamber and a fuel outlet. The variable volume chamber forming means is for forming a variable volume chamber, a volume of which changes by the reciprocating movement of the plunger. The variable volume chamber is placed adjacent to a step surface of the plunger. The step surface of the plunger is located between a large diameter portion of the plunger, which has an end portion exposed to the pressurizing chamber and is slidable along an inner peripheral wall surface of the cylinder hole, and a small diameter portion of the plunger, which extend from the large diameter portion in the axial direction on a side opposite from the pressurizing chamber. The gas chamber is placed adjacent to the variable volume chamber on a side of the variable volume chamber, which is opposite from the cylinder hole.

The gas chamber may be formed in a recess of the pump body, which is configured into a generally annular form around the cylinder hole on a radially outer side of the cylinder hole. The gas chamber may include or may be formed at least by an inner blocking wall, an outer blocking wall and gas. The inner blocking wall borders on the variable volume chamber and contacts fuel in the variable volume chamber. The outer blocking wall is opposed to the inner blocking wall. The gas fills a space that is defined between the inner blocking wall and the outer blocking wall, and this space may be an open space or closed space. A seal member may be installed to the small diameter portion of the plunger to surround the small diameter portion in a circumferential direction. The variable volume chamber forming means may include at least one or all of the step surface of the plunger, an outer peripheral wall of the small diameter portion, the inner peripheral wall of the cylinder hole of the pump body, an end portion of the seal member, a wall surface of the inner blocking wall and a wall surface of the recess of the pump body.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with additional objectives, features and advantages thereof, will be best understood from the following description, the appended claims and the accompanying drawings in which:

FIG. 1 is a schematic longitudinal cross sectional view of a high pressure pump according to a first embodiment of the present invention;

FIG. 2 is an enlarged schematic cross-sectional view showing a plunger arrangement of the high pressure pump shown in FIG. 1;

FIG. 3 is an enlarged schematic cross-sectional view showing a plunger arrangement of a high pressure pump according to a second embodiment of the present invention;

FIG. 4 is an enlarged schematic cross-sectional view showing a plunger arrangement of a high pressure pump according to a third embodiment of the present invention; and

FIG. 5 is an enlarged schematic cross-sectional view showing a plunger arrangement of a high pressure pump according to a fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Various embodiments of the present invention will be described with reference to the accompanying drawings.

First Embodiment

FIG. 1 shows a high pressure pump according to a first embodiment of the present invention. FIG. 2 shows a plunger arrangement of the high pressure pump.

The high pressure pump 1 of the present embodiment will be described with reference to FIG. 1.

The high pressure pump 1 is provided in a fuel supply system, which supplies fuel to an internal combustion engine of a vehicle (e.g., an automobile). The fuel, which is drawn from a fuel tank, is pressurized by the high pressure pump 1 and is stored in a delivery pipe. The fuel is injected from each corresponding injector, which is connected to the delivery pipe, into a corresponding cylinder of the internal combustion engine.

The high pressure pump 1 includes a pump body 10, a plunger arrangement 20, a damper chamber 40, an intake valve arrangement 50, an electromagnetic drive arrangement 60 and a discharge valve arrangement 70.

(a) The pump body 10 and the plunger arrangement 20 will be described.

The pump body 10 has a cylinder hole 11 and a pressurizing chamber 12, which are communicated with each other and are formed integrally in the pump body 10. A recess 13, which is configured into a generally annular form, is formed around the cylinder hole 11 on a radially outer side of the cylinder hole 11, and a cylindrical tubular protrusion 10 a of the pump body 10, which is axially downwardly protrudes in FIG. 2, is radially interposed between the cylinder hole 11 and a space of the recess 13 located radially outward of the cylindrical tubular portion 10 a. Therefore, a lower end portion of the cylinder hole 11 is formed by the cylindrical tubular protrusion 10 a of the pump body 10.

The plunger arrangement 20 includes a plunger 21, a seal member 24, a seal element 25, a plunger spring 28 and a variable volume chamber 30.

The plunger 21 is received in the cylinder hole 11 such that the plunger 21 is adapted to be axially reciprocated in an axial direction of the plunger 21 in the cylinder hole 11. The plunger 21 has a large diameter portion 211 and a small diameter portion 212. One end portion of the large diameter portion 211 is connected the small diameter portion 212, and the other end portion of the large diameter portion 211 is exposed to the pressurizing chamber 12. The large diameter portion 211 is slidable along an inner peripheral wall of the cylinder hole 11. The small diameter portion 212 has an outer diameter smaller than that of the large diameter portion 211 and axially extends from the large diameter portion 211 on a side, which is axially opposite from the pressurizing chamber 12. The large diameter portion 211 and the small diameter portion 212 are coaxial with each other, and a step surface 213 is formed between the large diameter portion 211 and the small diameter portion 212. A spring seat 27 is installed to one end portion 22 of the small diameter portion 212, which is opposite from the large diameter portion 211.

The seal member 24 is installed around the small diameter portion 212 of the plunger 21 such that the seal member 24 surrounds the small diameter portion 212 in a circumferential direction on a radially outer side of the small diameter portion 212. The seal member 24 includes a ring (Teflon ring, the name “Teflon” being a registered trademark of DuPont for its brand of fluoropolymer resins) and an O-ring. The ring is placed on a radially inner side and slidably contacts an outer peripheral surface of the small diameter portion 212, and the O-ring is placed on a radially outer side of the ring. The seal member 24 limits a thickness of a fuel film, which is formed around the small diameter portion 212, and also limits leakage of fuel toward the engine caused by the slide movement of the plunger 21.

The seal element 25 is installed around a portion of the small diameter portion 212, which is located on the spring seat 27 side of the seal member 24, such that the seal element 25 surrounds the small diameter portion 212 in the circumferential direction on the radially outer side of the small diameter portion 212. The seal element 25 is configured into a generally annular form. A portion of the seal element 25 is installed to and is secured to the recess 13 of the pump body 10. Another portion of the seal element 25 contacts both of one end portion of the seal member 24, which is axially located on the spring seat 27 side, and a radially outer end portion of the seal member 24, i.e., an outer peripheral portion of the seal member 24, which is radially located on the side opposite from the small diameter portion 212. In this way, the seal element 25 serves as a holder, which securely holds the seal member 24.

An oil seal 26 is installed to one end portion of the seal element 25, which is axially located on the spring seat 27 side. The oil seal 26 surrounds the small diameter portion 212 in the circumferential direction. The oil seal 26 slidably contacts an outer peripheral surface of the small diameter portion 212. The oil seal 26 limits a thickness of an oil film, which is formed around the small diameter portion 212, and limits leakage of the oil caused by the slide movement of the plunger 21.

The spring seat 27 is securely held by the lower end portion 22 of the plunger 21. One end portion of the plunger spring 28 is engaged to the spring seat 27. The other end portion of the plunger spring 28 is engaged to a predetermined end surface of the seat element 25, which is fixed to the pump body 10. Thereby, the seal element 25 also functions as an engaging member of the plunger spring 28.

The plunger spring 28, which is engaged to the seal element 25 and the spring seat 27 at the opposite ends, respectively, of the plunger spring 28, functions as a return spring of the plunger 21 to urge the plunger 21 against a tapped (not shown). The plunger 21 is urged against the cam of the camshaft through the tappet by the returning spring function of the plunger spring 28, i.e., the urging force of the plunger spring 28, so that the plunger 21 is axially reciprocated in the cylinder hole 11 upon the rotation of the camshaft. The volume of the pressurizing chamber 12 is changed by the reciprocating movement of the plunger 21, so that the fuel is drawn into and pressurized in the pressurizing chamber 12.

The variable volume chamber 30 is formed by a generally annular space, which is bounded by the step surface 213 of the plunger 21, the outer peripheral wall of the small diameter portion 212, the inner peripheral wall of the cylinder hole 11 of the pump body 10, a wall surface of the recess 13 (including an outer peripheral wall surface of the cylindrical tubular protrusion 10 a of the pump body 10), and the other end portion of the seal member 24 axially located on the pressurizing chamber 12 side. The variable volume chamber 30, which is configured into the generally annular form, surrounds the cylinder hole 11. The variable volume chamber 30 is in fluid communication with the damper chamber 40 through a return passage 31, which is formed in the pump body 10.

A gas chamber 32 is located adjacent to the variable volume chamber 30. The gas chamber 32 includes an inner blocking wall 33, which is located adjacent to the variable volume chamber 30. The inner blocking wall 33 is made of a resiliently deformable member. One end portion 331 of the inner blocking wall 33, which is axially located on the side opposite from the damper chamber 40, extends in a direction generally perpendicular to the central axis of the cylinder hole 11. Furthermore, the other end portion 332 of the inner blocking wall 33, which is axially located on the damper chamber 40 side, extends in a direction generally parallel to the central axis of the cylinder hole 11. A peripheral wall of the one end portion 331 of the inner blocking wall 33 is welded to an inner peripheral surface of the seal element 25 at a welding portion 34 a all around the one end portion 331 in the circumferential direction (i.e., by the welding-all-around). An outer peripheral wall of the other end portion 332 of the inner blocking wall 33 is welded to the inner peripheral surface of the seal element 25 at a welding portion 34 b all around the other end portion 332 in the circumferential direction.

A space 37, which is defined between the inner blocking wall 33 and the seal element 25, is filled with nitrogen gas 35 and is airtightly sealed, so that the space 37 is a closed space filled with the nitrogen gas 35.

The inner blocking wall 33, the seal element (serving as an outer blocking wall) 25 and the nitrogen gas 35 airtightly sealed in the space 37 therebetween form the gas chamber 32.

A wall surface of the one end portion 331 of the inner blocking wall 33, which is axially located on the pressurizing chamber 12 side, is axially opposed to the step surface 213 of the plunger 21. Therefore, the one end portion 331 of the inner blocking wall 33 functions as a stopper, which limits the reciprocating movement of the plunger 21 in the cylinder hole 11, particularly the downward movement of the plunger 21 in the cylinder hole 11 from the top dead center toward the bottom dead center thereof.

Furthermore, another wall surface of the one end portion 331 of the inner blocking wall 33, which is axially located on the spring seat 27 side, contacts the other end portion of the seal member 24, which is located on the pressurizing chamber 12 side. Therefore, the one end portion 331 of the inner blocking wall 33 functions as a holder, which securely holds the seal member 24. Specifically, the inner blocking wall 33, which contacts the other end portion of the seal member 24 axially located on the pressurizing chamber 12 side, cooperates with the seal element 25, which contacts both of the one end portion of the seal member 24 axially located on the spring seat 27 side and the outer peripheral portion of the seal member 24 radially located on the side opposite from the small diameter portion 212, to function as the holder, which securely holds, i.e., axially clamps the seal member 24.

(b) Next, the damper chamber 40 will be described.

The damper chamber 40 is formed by a recess 41, a cover 42 and a damper unit 43.

The other end portion of the pump body 10, which is axially opposite from the cylinder hole 11, is axially recessed toward the cylinder hole 11 side to form the recess 41. The cover 42, which is configured into a cup form (a tubular body having a bottom), is installed to the pump body 10 to cover the recess 41 and thereby to seal an inside of the recess 41 from an external atmosphere.

The damper unit 43 is placed in the damper chamber 40. The damper unit 43 includes a pulsation damper 44, a bottom side support portion 45 and a cover side support portion 46. The pulsation damper 44 includes two metal diaphragms 441, 442, which are opposed to each other and are joined together. The bottom side support portion 45 is placed at a bottom portion of the recess 41. The cover side support portion 46 is placed at the cover 42 side.

In the pulsation damper 44, gas of a predetermined pressure is sealed in an inside space, which is defined between the metal diaphragm 441 and the metal diaphragm 442. When the metal diaphragms 441, 442 are resiliently deformed in response to a change in the pressure of the fuel in the damper chamber 40, pressure pulsation of the fuel in the damper chamber 40 is damped (limited or alleviated).

A recess 47, which is configured to correspond with the bottom side support portion 45, is formed in the bottom portion of the recess 41 of the damper chamber 40. The bottom side support portion 45 is positioned by the recess 47. An opening of an inlet (not shown) is formed in the recess 47, so that the fuel, which is supplied from the low pressure pump, is supplied to a radially inner region of the bottom side support portion 45 through the inlet. Specifically, the fuel of the fuel tank is supplied to the damper chamber 40 from the fuel inlet through the fuel passage.

A wavy spring 48 is placed on the upper side of the cover side support portion 46. Therefore, in the installed state where the cover 42 is installed to the pump body 10, the wavy spring 48 urges the cover side support portion 46 toward the bottom side support portion 45. Thus, the pulsation damper 44 is secured such that the pulsation damper 44 is clamped between the cover side support portion 46 and the bottom side support portion 45 by a generally uniform clamping force, which is generally uniform along the entire circumference of the pulsation damper 44 and is applied from the cover side support portion 46 and the bottom side support portion 45.

(c) The intake valve arrangement 50 will now be described.

The intake valve arrangement 50 includes a supply passage 52, a valve body 53, a seat 54 and an intake valve 55.

The pump body 10 has a tubular portion 51, which extends in a direction that is generally perpendicular to the central axis of the cylinder hole 11. The supply passage 52 is formed in an inside of the tubular portion 51. The valve body 53 is received in the tubular portion 51 and is fixed by an engaging member. The seat 54 is formed in the inside of the valve body 53 such that the seat 54 has a tapered inner peripheral concave surface. The intake valve 55 is placed such that the intake valve 55 is opposed to the seat 54. The intake valve 55 is reciprocated such that the intake valve 55 is guided by an inner peripheral wall of a hole, which is formed in a bottom portion of the valve body 53. When the intake valve 55 is lifted from the seat 54, the supply passage 52 is opened. In contrast, when the intake valve 55 is seated against the seat 54, the supply passage 52 is closed with the intake valve 55.

A stopper 56 is fixed to an inner peripheral wall of the valve body 53 such that the stopper 56 limits movement of the intake valve in a valve opening direction (the right direction in FIG. 1) of the intake valve 55. A first spring 57 is placed between an inner portion of the stopper 56 and an end surface of the intake valve 55. The first spring 57 urges the intake valve 55 in a valve closing direction (the left direction in FIG. 1).

A plurality of tilted passages 58 is formed in the stopper 56 such that the tilted passages 58 are tilted relative to the axis of the stopper 56 and are arranged one after another in a circumferential direction. The fuel, which is supplied through the supply passage 52, is drawn into the pressurizing chamber 12 through the tilted passages 58. Furthermore, the supply passage 52 is communicated with the damper chamber 40 through a pressurizing side passage 59. Thereby, the damper chamber 40, the pressurizing side passage 59, the supply passage 52 and the tilted passages 58 cooperate together to form a low pressure fuel passage, which communicates between the inlet and the pressurizing chamber 12.

(d) The electromagnetic drive arrangement 60 will be described.

The electromagnetic drive arrangement 60 includes a connector 61, a stationary core 62, a movable core 63 and a flange 64.

The connector 61 includes a coil 611 and terminals 612. When an electric power is supplied to the coil 611 through the terminals 612, a magnetic field is generated from the coil 611. The stationary core 62 is made of a magnetic material and is received in the inside of the coil 611. The movable core 63 is made of a magnetic material and is opposed to the stationary core 62. The movable core 63 is adapted to axially reciprocate at a location radially inward of the flange 64.

The flange 64 is made of a magnetic material and is installed to the tubular portion 51 of the pump body 10. The flange 64 holds the connector 61 in corporation with the pump body 10 and closes an end portion of the tubular portion 51. A guide tube 65 is installed to an inner peripheral wall of a hole, which is formed in a center of the flange 64. A tubular member 66, which is made of a non-magnetic material, limits magnetic short circuit between the stationary core 62 and the flange 64.

A needle 67 is configured into a generally cylindrical tubular form and is guided by an inner peripheral wall of the guide tube 65 such that the needle 67 is adapted to be reciprocated along the inner peripheral wall of the guide tube 65. One end portion of the needle 67 is fixed to the movable core 63, and the other end portion of the needle 67 is contactable with an end surface of the intake valve 55, which is located on a side where the electromagnetic drive arrangement 60 is located.

A second spring 68 is placed between the stationary core 62 and the movable core 63. The second spring 68 urges the movable core 63 in the valve opening direction by an urging force, which is larger than an urging force of the first spring 57, which urges the intake valve 55 in the valve closing direction.

When the coil 611 is not energized, the movable core 63 and the stationary core 62 are spaced from each other by a resilient force of the second spring 68. Thereby, the needle 67, which is integrated with the movable core 63, is moved toward the intake valve 55 side to urge the intake valve 55 with the end surface of the needle 67, so that the intake valve 55 is opened.

(e) The discharge valve arrangement 70 will be described.

The discharge valve arrangement 70 includes a discharge passage 71 and a discharge valve device 80.

The discharge passage 71 is formed in the pump body 10 such that the discharge passage 71 extends in a direction that is generally perpendicular to the central axis of the cylinder hole 11. One end of the discharge passage 71 is communicated with the pressurizing chamber 12, and the other end of the discharge passage 71 is communicated with a fuel outlet 72. The discharge valve device 80 is installed to the discharge passage 71.

The discharge valve device 80 includes a discharge valve member 82, a spring 83 and an adjusting pipe 84.

The discharge valve member 82 is received in the pump body 10 such that the discharge valve member 82 is opposed to a valve seat 85 of the pump body 10.

The spring 83, which serves as an urging member, is received in the pump body 10 on a fuel outlet 72 side of the discharge valve member 82. One end portion of the spring 83 contacts an end surface (a right end surface in FIG. 1) of the discharge valve member 82. The adjusting pipe 84, which is configured into a cylindrical tubular form, is received in the pump body 10 on a fuel outlet 72 side of the spring 83. The adjusting pipe 84 serves as a support member such that the other end portion of the spring 83 is engaged to the adjusting pipe 84.

As discussed above, the discharge valve arrangement 70 includes the discharge valve device 80. The discharge valve device 80 includes the discharge valve member 82, the spring 83 and the adjusting pipe 84, and the discharge valve member 82 is urged by the urging force of the spring 83 that is engaged to the adjusting pipe 84 at the other end portion of the spring 83.

The discharge valve device 80 of the discharge valve arrangement 70 is operated as follows.

When the plunger 21 is moved upward in the cylinder hole 11, the pressure of the fuel in the pressurizing chamber 12 is increased. When the force, which is applied to the discharge valve member 82 by the fuel on the pressurizing chamber 12 side (the upstream side) of the discharge valve member 82, becomes larger than a sum of the resilient force of the spring 83 and the force of the fuel on the fuel outlet 72 side (the downstream side) of the discharge valve member 82, the discharge valve member 82 is lifted away from the valve seat 85. That is, the discharge valve device 80 is placed into a valve open state. In this way, the high pressure fuel, which is pressurized in the pressurizing chamber 12, is discharged to the fuel outlet 72 through the discharge passage 71.

In contrast, when the plunger 21 is moved downward in the cylinder hole 11, the pressure of the fuel in the pressurizing chamber 12 is decreased. When the force, which is applied to the discharge valve member 82 by the fuel on the upstream side of the discharge valve member 82, becomes larger than the sum of the resilient force of the spring 83 and the force of the fuel on the downstream side of the discharge valve member 82, the discharge valve member 82 is seated against the valve seat 85. That is, the discharge valve device 80 is placed into a valve closed state. In this way, it is possible to limit a backflow of the fuel from the downstream side of the discharge valve member 82 into the pressurizing chamber 12 located on the upstream side of the discharge valve member 82.

As discussed above, the discharge valve device 80 of the discharge valve arrangement 70 serves as a check valve, which limits the backflow of the high pressure fuel that is discharged from the pressurizing chamber 12 toward the fuel outlet 72.

Next, the operation of the high pressure pump 1 will be described.

(1) Intake Stroke

When the plunger 21 is moved downward from the top dead center toward the bottom dead center in the cylinder hole 11 by the rotation of the camshaft, the volume of the pressurizing chamber 12 is increased, and the fuel in the pressurizing chamber 12 is depressurized. At this time, in the discharge valve arrangement 70, the discharge valve member 82 of the discharge valve device 80 is seated against the valve seat 85, so that the discharge passage 71 is closed. Furthermore, in the intake valve arrangement 50, the intake valve 55 is moved in the right direction in FIG. 1 due to the pressure difference between the pressurizing chamber 12 and the supply passage 52 against the urging force of the first spring 57, so that the intake valve 55 is placed in the valve open state. At this time, the energization of the coil 611 of the electromagnetic drive arrangement 60 is stopped, so that the movable core 63 and the needle 67 integrated therewith are moved by the urging force of the second spring 68 in the right direction in FIG. 1. Therefore, the needle 67 and the intake valve 55 contact with each other, and the intake valve 55 is held in the valve open state. Thereby, the fuel is drawn from the supply passage 52 into the pressurizing chamber 12.

In the intake stroke, the plunger 21 is moved downward, so that the volume of the variable volume chamber 30 is decreased. Thus, the fuel of the variable volume chamber 30 is outputted to the damper chamber 40 through the return passage 31.

In this instance, a ratio between the cross-sectional area of the large diameter portion 211 and the cross-sectional area of the variable volume chamber 30 is generally 1:0.6. Thus, a ratio between the amount of increase in the volume of the pressurizing chamber 12 and the amount of decrease in the volume of the variable volume chamber 30 is generally 1:0.6. Therefore, about 60% of the fuel, which is drawn into the pressurizing chamber 12, is supplied from the variable volume chamber 30, and about 40% of the remaining fuel is drawn from the fuel inlet. In this way, an intake efficiency of fuel into the pressurizing chamber 12 is improved.

(2) Metering Stroke

When the plunger 21 is moved upward from the bottom dead center toward the top dead center in the cylinder hole 11 by the rotation of the camshaft, the volume of the pressurizing chamber 12 is decreased. At this time, the energization of the coil 611 is stopped until the predetermined timing (predetermined time point), so that the needle 67 and the intake valve 55 are urged by the urging force of the second spring 68 in the right direction in FIG. 1 and are thereby placed at the right side position in FIG. 1. Thereby, the supply passage 52 is kept in the open state. Thus, the low pressure fuel, which is once drawn into the pressurizing chamber 12, is returned to the supply passage 52. As a result, the pressure of the pressurizing chamber 12 is not increased.

In the metering stroke, the plunger 21 is moved upward, so that the volume of the variable volume chamber 30 is increased. Thus, the fuel of the damper chamber 40 flows into the variable volume chamber 30 through the return passage 31.

At this time, about 60% of the volume of the low pressure fuel, which is discharged from the pressurizing chamber 12 toward the damper chamber 40 side, is drawn into the variable volume chamber 30 from the damper chamber 40. Thereby, about 60% of the fuel pressure pulsation is reduced.

(3) Pressurizing Stroke

At the predetermined timing (predetermined time point) during the movement of the plunger from the bottom dead center toward the top dead center in the cylinder hole 11, the coil 611 is energized. Then, a magnetic attractive force is generated between the stationary core 62 and the movable core 63 due to the generation of the magnetic field from the coil 611. When this magnetic attractive force becomes larger than a difference between the resilient force of the second spring 68 and the resilient force of the first spring 57, the movable core 63 and the needle 67 are moved toward the stationary core 62 side (in the left direction in FIG. 1). Thereby, the urging force of the needle 67 against the intake valve 55 is released. The intake valve 55 is moved toward the seat 54 side by the resilient force of the first spring 57 and the force generated by the flow of the low pressure fuel, which is outputted from the pressurizing chamber 12 toward the damper chamber 40. Thus, the intake valve 55 is seated against the seat 54, so that the supply passage 52 is closed.

Since the time of seating the intake valve 55 against the seat 54, the pressure of the fuel in the pressurizing chamber 12 is increased as the plunger 21 is moved upward toward the top dead center of the plunger 21. In the discharge valve arrangement 70, the discharge valve member 82 of the discharge valve device 80 is opened when the force, which is applied to the discharge valve member 82 by the pressure of the fuel on the upstream side of the discharge valve member 82, becomes larger than a sum of the urging force of the spring 83 and the force, which is applied to the discharge valve member 82 by the pressure of the fuel on the downstream side of the discharge valve member 82. In this way, the high pressure fuel, which is pressurized in the pressurizing chamber 12, is discharged from the fuel outlet 72 through the discharge passage 71.

In the middle of the pressurizing stroke, the energization of the coil 611 is stopped. The force, which is applied to the intake valve 55 from the pressure of the fuel in the pressurizing chamber 12, is larger than the urging force of the second spring 68, so that the intake valve 55 is kept in the valve closed state.

The high pressure pump 1 repeats the intake stroke, the metering stroke and the pressurizing stroke, so that the fuel, which is required by the internal combustion engine, is pressurized and is discharged from the high pressure pump 1.

When the timing of energizing the coil 611 is shifted to earlier timing, the time period of the metering stroke is shortened, and the time period of the pressurizing stroke is lengthened. Therefore, the fuel, which is returned from the pressurizing chamber 12 to the supply passage 52, is reduced, and the fuel, which is outputted from the discharge passage 71, is increased. In contrast, when the timing of energizing the coil 611 is shifted to later timing, the time period of the metering stroke is lengthened, and the time period of the discharge stroke is shortened. Therefore, the fuel, which is returned from the pressurizing chamber 12 to the supply passage 52, is increased, and the fuel, which is outputted from the discharge passage 71, is decreased.

As discussed above, the quantity of fuel, which is discharged from the high pressure pump 1, is controlled to the required quantity, which is required by the internal combustion engine, by controlling the timing of energizing the coil 611.

Next, advantages of the present embodiment will be described.

In the present embodiment, the gas chamber 32 is placed at the location adjacent to the variable volume chamber 30 of the high pressure pump 1. The gas chamber 32 is formed by the inner blocking wall 33 placed adjacent to the variable volume chamber 30, the seal element (serving as the outer blocking wall) 25 and the nitrogen gas 35 sealed in the space 37 between the inner blocking wall 33 and the seal element 25. Therefore, even when the heat of an engine head, which is heated to the high temperature and is placed adjacent to the cam that drives the plunger to reciprocate the same, is conducted toward the fuel in the variable volume chamber 30, the influence of the heat from the engine head is blocked or alleviated by the nitrogen gas 35 in the gas chamber 32, which is placed in the heat conduction path between the engine head and the variable volume chamber 30. Furthermore, even when the high temperature lubricating oil (including engine oil) is scattered from the cam or its adjacent area and is adhered to the outer wall of the seal element 25 to cause conduction of the heat from the adhered high temperature lubricating oil to the fuel in the variable volume chamber 30, the influence of the heat of the adhered high temperature lubricating oil is blocked or alleviated by the nitrogen gas 35 in the gas chamber 32, which is placed between the adhered high temperature lubricating oil and the fuel in the variable volume chamber 30.

Here, a thermal conductivity of the nitrogen gas 35 in the gas chamber 32 is 25.76 mW/(m·K) under the temperature of 25 degrees Celsius and the atmospheric pressure of 1 atm. This thermal conductivity of the nitrogen gas 35 is much lower than that of the metal material of the high pressure pump 1 and of the other solid materials. Therefore, the nitrogen gas 35 can effectively block or limit the conduction of the heat to the fuel in the variable volume chamber 30.

Furthermore, the peripheral wall of the one end portion 331 of the inner blocking wall 33 of the gas chamber 32 is welded to the inner peripheral surface of the seal element 25 at the welding portion 34 a all around the one end portion 331 in the circumferential direction, and the outer peripheral wall of the other end portion 332 of the inner blocking wall 33 is welded to the inner peripheral surface of the seal element 25 at the welding portion 34 b all around the other end portion 332 in the circumferential direction. Thereby, the nitrogen gas 35 in the gas chamber 32 is sealed in the airtight state in the space 37. Thus, the heat conduction blocking function (or the heat conducting limiting function) of the nitrogen gas 35 in the gas chamber 32 is stably maintained.

In this way, the increasing of the temperature of the fuel in the variable volume chamber 30 to the high temperature can be limited by the heat conduction blocking function (or the heat conducting limiting function) of the nitrogen gas 35 in the gas chamber 32, which is adjacent to the variable volume chamber 30, and thereby the vaporization of the fuel in the variable volume chamber 30 can be limited. Thus, it is possible to limit the occurrence of the operational malfunction of the high pressure pump 1, i.e., the difficulty of drawing the fuel by the high pressure pump 1 caused by the vaporization of the fuel in the variable volume chamber 30.

Furthermore, at the time of repeating the intake stroke, the metering stroke and the pressurizing stroke at the high pressure pump 1 of the present embodiment, the fuel in the variable volume chamber 30 is outputted to the damper chamber 40 and is then returned to the damper chamber 40 in response to the moving up and moving down of the plunger 21. At this time, the inner blocking wall 33, which is resiliently deformable and is interposed between the fuel in the variable volume chamber 30 and the nitrogen gas 35 in the gas chamber 32, functions as the pulsation damper for the fuel in the variable volume chamber 30. Thus, the pressure pulsation of the fuel in the variable volume chamber 30 is reduced or minimized.

The fuel pressure pulsation reducing effect of the inner blocking wall 33, which functions as the pulsation damper for the fuel in the variable volume chamber 30, and the fuel pressure pulsation reducing effect, which is implemented by the damper chamber 40, can further reduce the pressure pulsation of the low pressure fuel, which is supplied to the pressurizing chamber 12. Thereby, the appropriate operation of the high pressure pump 1 can be more effectively ensured.

Furthermore, the one end portion 331 of the inner blocking wall 33, which is the component of the gas chamber 32, is installed such that the wall surface of the one end portion 331 of the inner blocking wall 33, which is axially located on the pressurizing chamber 12 side, is axially opposed to the step surface 213 of the plunger 21, and the wall surface of the one end portion 331 of the inner blocking wall 33, which is axially located on the side opposite from the pressurizing chamber 12, contacts the other end portion of the seal member 24, which is axially located on the pressurizing chamber 12 side. Therefore, the inner blocking wall 33 functions as the stopper of the plunger 21 at the time of reciprocating the plunger 21 in the cylinder hole 11. Also, the inner blocking wall 33 cooperates with the seal element 25, which contacts both of the one end portion of the seal member 24 axially located on the spring seat 27 side and the outer peripheral portion of the seal member 24 radially located on the side opposite from the small diameter portion 212, to function as the holder, which securely holds, i.e., axially clamps the seal member 24.

That is, the inner blocking wall 33 of the gas chamber 32 has the function, which is previously implemented in a plunger stopper in a previously proposed high pressure pump. Therefore, the plunger stopper, which is used in the previously proposed high pressure pump, is not required in the high pressure pump 1 of the present embodiment. Thus, the number of the components of the high pressure pump 1 can be reduced, and thereby the manufacturing costs of the high pressure pump 1 can be reduced.

Furthermore, in the present embodiment, the seal element 25, which is also employed in the previously proposed high pressure pump, is used as the outer blocking wall of the gas chamber 32, so that it is possible to limit an increase in the number of components, which are required to form the gas chamber 32. Therefore, it is possible to limit an increase in the manufacturing costs of the high pressure pump 1.

Second Embodiment

FIG. 3 shows a plunger arrangement of a high pressure pump according to a second embodiment of the present invention. In the following embodiments, components, which are similar to those of the first embodiment, will be indicated by the same reference numerals and will not be redundantly described.

The plunger arrangement 20 of the high pressure pump 2 of the present embodiment will be described with referent o FIG. 3. The other remaining structure of the high pressure pump 2 of the present embodiment, which is other than the plunger arrangement 20, is the same as that of the high pressure pump 1 of the first embodiment shown in FIG. 1 and thereby will not be described further.

Similar to the first embodiment, the plunger arrangement 20 includes the plunger 21, the seal member 24, the seal element 25, the plunger spring 28 and the variable volume chamber 30.

In the present embodiment, a gas chamber 32A, which is adjacent to the variable volume chamber 30 of the high pressure pump 2, includes an inner blocking wall 33A in place of the inner blocking wall 33 of the first embodiment. Similar to the first embodiment, the inner blocking wall 33A is the resiliently deformable member and functions as the pulsation damper for the fuel in the variable volume chamber 30.

Similar to the first embodiment, one end portion 331 a of the inner blocking wall 33A, which is axially located on the side opposite from the damper chamber 40, extends in the direction generally perpendicular to the central axis of the cylinder hole 11. Furthermore, a peripheral wall of the one end portion 331 a of the inner blocking wall 33A is welded to the inner peripheral surface of the seal element 25 at the welding portion 34 a all around the one end portion 331 a in the circumferential direction like in the first embodiment. Unlike the first embodiment, the other end portion 332 a of the inner blocking wall 33A, which is axially located on the damper chamber 40 side, extends in a direction generally perpendicular to the central axis of the cylinder hole 11. A peripheral wall of the other end portion 332 a of the inner blocking wall 33A is welded to the inner peripheral surface of the seal element 25 at a welding portion 34 c, which is different from the welding portion 34 b of the first embodiment, all around the other end portion 332 a in the circumferential direction.

Similar to the first embodiment, the nitrogen gas 35 is filled into and is sealed in the space 37, which is defined between the inner blocking wall 33A and the seal element (serving as the outer blocking wall) 25.

In this way, the inner blocking wall 33A, which is configured into the shape that is different from the inner blocking wall 33 of the first embodiment, the seal element (serving as the outer blocking wall) 25 and the nitrogen gas 35 airtightly sealed in the space 37 between the inner blocking wall 33A and the seal element 25 form the gas chamber 32A of the present embodiment.

Furthermore, similar to the first embodiment, the one end portion 331 a of the inner blocking wall 33A, which is the component of the gas chamber 32A, is installed such that the wall surface of the one end portion 331 a of the inner blocking wall 33A, which is axially located on the pressurizing chamber 12 side, is axially opposed to the step surface 213 of the plunger 21, and the wall surface of the one end portion 331 a of the inner blocking wall 33A, which is axially located on the side opposite from the pressurizing chamber 12, contacts the other end portion of the seal member 24, which is axially located on the pressurizing chamber 12 side. Therefore, similar to the first embodiment, the inner blocking wall 33A has the function similar to that of the plunger stopper of the previously proposed high pressure pump.

The other remaining structure of the plunger arrangement 20 of the present embodiment, which is other than the gas chamber 32A, is the same as that of the first embodiment and thereby will not be described further.

Next, advantages of the present embodiment will be described.

In the present embodiment, the gas chamber 32, which is placed adjacent to the variable volume chamber 30 of the high pressure pump 2, is formed by the inner blocking wall 33A placed adjacent to the variable volume chamber 30, the seal element (serving as the outer blocking wall) 25 and the nitrogen gas 35 sealed in the space 37 between the inner blocking wall 33 and the seal element 25.

Therefore, similar to the first embodiment, the increasing of the temperature of the fuel in the variable volume chamber 30 to the high temperature can be limited by the heat conduction blocking function (or the heat conducting limiting function) of the nitrogen gas 35 in the gas chamber 32A, and thereby the vaporization of the fuel in the variable volume chamber 30 can be limited. Thus, it is possible to limit the occurrence of the operational malfunction of the high pressure pump 2 caused by the vaporization of the fuel in the variable volume chamber 30.

Furthermore, according to the present embodiment, the shape of the inner blocking wall 33A of the gas chamber 32A and the welding portion 34 c of the inner blocking wall 33A, which is welded to the seal element 25, are different from the shape of the inner blocking wall 33 of the gas chamber 32 and the welding portion 34 b of the inner blocking wall 33, which is welded to the seal element 25, of the first embodiment.

Specifically, in the first embodiment, the other end portion 332 of the inner blocking wall 33 of the gas chamber 32 extends in the direction generally parallel to the central axis of the cylinder hole 11, and the peripheral wall of the other end portion 332 of the inner blocking wall 33 is welded to the inner peripheral surface of the seal element 25 at the welding portion 34 b all around the other end portion 332 in the circumferential direction. In contrast, according to the present embodiment, the other end portion 332 a of the inner blocking wall 33A of the gas chamber 32A extends in the direction generally perpendicular to the central axis of the cylinder hole 11, and the peripheral wall of the other end portion 332 a of the inner blocking wall 33A is welded to the inner peripheral surface of the seal element 25 at the welding portion 34 c all around the other end portion 332 a in the circumferential direction.

When the inner blocking wall 33A is configured into the above-described shape, which is different from that of the inner blocking wall 33 of the first embodiment, the volume of the gas chamber 32A (more specifically, the volume of the space 37) is increased in comparison to the volume of the gas chamber 32 of the first embodiment, as evident from FIGS. 2 and 3. Thereby, the volume of the nitrogen gas 35, which is sealed in the gas chamber 32A is increased in comparison to the volume of the nitrogen gas 35, which is sealed in the gas chamber 32 of the first embodiment. Thus, the heat conduction blocking function (or the heat conducting limiting function) of the nitrogen gas 35 in the gas chamber 32A is further enhanced in the second embodiment in comparison to the first embodiment. Thus, it is possible to further limit the occurrence of the operational malfunction of the high pressure pump 2 caused by the vaporization of the fuel in the variable volume chamber 30.

The other advantages of the present embodiment are similar to those of the first embodiment. These other advantages of the present embodiment include, for example, the reduction of the pressure pulsation of the low pressure fuel supplied to the pressurizing chamber 12 implemented by the fuel pressure pulsation reducing effect of the inner blocking wall 33A, which serves as the pulsation damper for the fuel in the variable volume chamber 30.

Third Embodiment

FIG. 4 shows a plunger arrangement of a high pressure pump according to a third embodiment of the present invention.

The plunger arrangement 20 of the high pressure pump 3 of the present embodiment will be described with referent o FIG. 4. The other remaining structure of the high pressure pump 2 of the present embodiment, which is other than the plunger arrangement 20, is the same as that of the high pressure pump 1 of the first embodiment shown in FIG. 1 and thereby will not be described further.

Similar to the first embodiment, the plunger arrangement 20 includes the plunger 21, the seal member 24, the seal element 25, the plunger spring 28 and the variable volume chamber 30. Unlike the first embodiment, the plunger arrangement 20 of the present embodiment includes a plunger stopper 23.

The plunger stopper 23 is configured into an annular form and surrounds the small diameter portion 212 of the plunger 21. An end surface of the plunger stopper 23, which is axially located on the pressurizing chamber 12 side, is axially recessed toward the spring seat 27 side to form a recess. An end surface 231 of the plunger stopper 23, which is radially located on the outer side of the recess and is axially directed to the pressurizing chamber 12 side (i.e., is axially located on the pressurizing chamber 12 side), is joined to or securely connected to the pump body 10. An end surface 232 of the recess of the plunger stopper 23, which is directed to the pressurizing chamber 12 side (i.e., is axially located on the pressurizing chamber 12 side), is axially opposed to the step surface 213, which is formed between the large diameter portion 211 and the small diameter portion 212 of the plunger 21.

Therefore, the end surface 232 of the plunger stopper 23, which is axially opposed to the step surface 213 of the plunger 21, functions as the stopper, which is adapted to abut against the step surface 213 of the plunger 21 and thereby to limit the reciprocating movement of the plunger 21 in the cylinder hole 11, particularly the downward movement of the plunger 21 in the cylinder hole 11 in a direction away from the top dead center toward the bottom dead center.

A plurality of groove passages (only one is shown in FIG. 4) 23 a, which serve as radial passages, is formed in the plunger stopper 23 to radially extend from the interior of the recess to the outer peripheral edge of the plunger stopper 23 to enable fluid communication therebetween. The groove passages 23 a of the plunger stopper 23 communicate between one area (radially inner area) of the variable volume chamber 30, which is defined between the step surface 213 of the plunger 21 and the plunger stopper 23 upon lifting of the step surface 213 of the plunger 21 from the end surface 232 of the plunger stopper 23, to another area (radially outer area) of the variable volume chamber 30, which is communicated with the damper chamber 40.

The seal member 24 is installed around the small diameter portion 212 of the plunger 21 at an axial location, which is on the spring seat 27 side of the plunger stopper 23, such that the seal member 24 surrounds the small diameter portion 212 in the circumferential direction. The other end portion of the seal member 24, which is axially located on the pressurizing chamber 12 side, contacts a wall surface of the plunger stopper 23, which is axially located on the spring seat 27 side. Therefore, the plunger stopper 23 cooperates with the seal element 25, which contacts both of the one end portion of the seal member 24 axially located on the spring seat 27 side and the radially outer portion of the seal member 24 radially located on the side opposite from the small diameter portion, to function as the holder, which securely holds, i.e., axially clamps the seal member 24.

The seal element 25, the plunger spring 28 and the variable volume chamber 30 are arranged in a manner similar to that of the first embodiment.

In the present embodiment, a gas chamber 32B, which is adjacent to the variable volume chamber 30 of the high pressure pump 3, includes an inner blocking wall 33B in place of the inner blocking wall 33 of the first embodiment. Similar to the first embodiment, the inner blocking wall 33B is the resiliently deformable member and functions as the pulsation damper for the fuel in the variable volume chamber 30.

Unlike the first embodiment, one end portion 331 b of the inner blocking wall 33B, which is axially located on the side opposite from the damper chamber 40, extends in a direction generally parallel to the central axis of the cylinder hole 11. Furthermore, a peripheral wall of the one end portion 331 b of the inner blocking wall 33B is welded to the inner peripheral surface of the seal element 25 at the welding portion 34 a all around the one end portion 331 b in the circumferential direction like in the first embodiment.

In the present embodiment, due to the provision of the plunger stopper 23, the shape of the one end portion 331 b of the inner blocking wall 33B is different from that of the first embodiment. For example, the peripheral wall of the one end portion 331 b of the inner blocking wall 33B contacts an outer peripheral wall of the plunger stopper 23.

Similar to the first embodiment, the other end portion 332 b of the inner blocking wall 33B, which is axially located on the damper chamber 40 side, extends in the direction generally parallel to the central axis of the cylinder hole 11. A peripheral wall of the other end portion 332 b of the inner blocking wall 33B is welded to the inner peripheral surface of the seal element 25 at the welding portion 34 b all around the other end portion 332 b in the circumferential direction, like in the first embodiment.

Similar to the first embodiment, the nitrogen gas 35 is sealed into the space 37, which is held between the inner blocking wall 33B and the seal element (serving as the outer blocking wall) 25.

The inner blocking wall 33B, the seal element (serving as the outer blocking wall) 25 and the nitrogen gas 35 airtightly sealed therebetween form the gas chamber 32B of the present embodiment.

Next, advantages of the present embodiment will be described.

In the present embodiment, the gas chamber 32B, which is placed adjacent to the variable volume chamber 30 of the high pressure pump 3, is formed by the inner blocking wall 33B placed adjacent to the variable volume chamber 30, the seal element (serving as the outer blocking wall) 25 and the nitrogen gas 35 sealed in the space 37 between the inner blocking wall 33B and the seal element 25. Therefore, similar to the first embodiment, the increasing of the temperature of the fuel in the variable volume chamber 30 to the high temperature can be limited by the heat conduction blocking function (or the heat conducting limiting function) of the nitrogen gas 35 in the gas chamber 32B, and thereby the vaporization of the fuel in the variable volume chamber 30 can be limited. Thus, it is possible to limit the occurrence of the operational malfunction of the high pressure pump 3 caused by the vaporization of the fuel in the variable volume chamber 30.

Furthermore, similar to the first embodiment, the inner blocking wall 33B of the gas chamber 32B, which is resiliently deformable, functions as the pulsation damper to reduce or minimize the fuel pressure pulsation of the fuel in the variable volume chamber 30. Therefore, it contributes to the reduction or minimization of the pressure pulsation of the low pressure fuel, which is supplied to the pressurizing chamber 12.

In the present embodiment, the plunger stopper 23 is provided. The plunger stopper 23 functions as the stopper for the reciprocating movement of the plunger 21. Also, the plunger stopper 23 cooperates with the seal element 25 to function as the holder, which securely holds, i.e., axially clamps the seal member 24. Therefore, the functions, which are implemented by the inner blocking wall 33 of the first embodiment, are not implemented by the inner blocking wall 33B of the present embodiment.

Thereby, even in the high pressure pump 3 of the present embodiment, the advantages similar to those of the first embodiment can be achieved by providing the gas chamber 32B, which is formed by the inner blocking wall 33B, which is placed adjacent to the variable volume chamber 30 and functions as the pulsation damper, the seal element (serving as the outer blocking wall) 25 and the nitrogen gas 35 sealed in the space 37 formed between the inner blocking wall 33 and the seal element 25.

Fourth Embodiment

FIG. 5 shows a plunger arrangement of a high pressure pump according to a fourth embodiment of the present invention.

The plunger arrangement 20 of the high pressure pump 4 of the present embodiment will be described with referent o FIG. 5. The other remaining structure of the high pressure pump 4 of the present embodiment, which is other than the plunger arrangement 20, is the same as that of the high pressure pump 1 of the first embodiment shown in FIG. 1 and thereby will not be described further.

Similar to the third embodiment, the plunger arrangement 20 includes the plunger 21, the plunger stopper 23, the seal member 24, the seal element 25, the plunger spring 28 and the variable volume chamber 30.

A gas chamber 32C, which is placed adjacent to the variable volume chamber 30 of the high pressure pump 4 of the present embodiment, includes the seal element 25, which now serves as the inner blocking wall, in place of the inner blocking wall 33B of the third embodiment. The gas chamber 32C further includes an outer blocking wall 36 in place of the seal element 25, which serves as the outer blocking wall in the third embodiment. The outer blocking wall 36 is made of a heat insulation member. One end portion 361 of the outer blocking wall 36, which is located on the side opposite from the damper chamber 40, extends in a direction that is generally parallel to the central axis of the cylinder hole 11. The other end portion 362 of the outer blocking wall 36, which is located on the side where the damper chamber 40 is located, extends in a direction generally perpendicular to the central axis of the cylinder hole 11. A peripheral wall of the one end portion 361 of the outer blocking wall 36 is welded to the inner peripheral surface of the seal element 25 at a welding portion 34 d all around the one end portion 361 in the circumferential direction. An outer peripheral wall of the other end portion 362 of the outer blocking wall 36 is welded to the inner peripheral surface of the seal element 25 at a welding portion 34 e all around the other end portion 362 in the circumferential direction.

The nitrogen gas 35 is sealed into the space 37, which is held between the seal element (serving as the inner blocking wall) 25 and the outer blocking wall 36.

In this way, the gas chamber 32C of the present embodiment is formed by the seal element (serving as the inner blocking wall) 25, the outer blocking wall 36 and the nitrogen gas 35 sealed in the space 37 formed between the seal element 25 and the outer blocking wall 36.

The other remaining structure of the high pressure pump 4 of the present embodiment, which is other than the gas chamber 32C of the plunger arrangement 20, is the same as that of the high pressure pump 3 of the third embodiment and thereby will not be described further.

Next, advantages of the present embodiment will be described.

In the present embodiment, the gas chamber 32C, which is placed adjacent to the variable volume chamber 30 of the high pressure pump 4, is made by the seal element (serving as the inner blocking wall) 25, the outer blocking wall 36 made of the heat insulation member, and the nitrogen gas 35 sealed in the space 37 formed between the seal element 25 and the outer blocking wall 36.

Therefore, in the present embodiment, similar to the third embodiment, the heat conduction blocking function (or the heat conduction limiting function) can be implemented by the nitrogen gas 35 in the gas chamber 32C, and thereby it is possible to limit the occurrence of the operational malfunction of the high pressure pump 4 caused by the vaporization of the fuel in the variable volume chamber 30.

Furthermore, the outer blocking wall 36 is made of the heat insulation member. Therefore, the heat conduction blocking function (or the heat conduction limiting function) of the outer blocking wall 36 is implemented in addition to the heat conduction blocking function (or the heat conduction limiting function) of nitrogen gas 35. As a result, the heat conduction blocking function of the entire gas chamber 32C is further increased, and thereby the operational malfunction of the high pressure pump 4 can be more effectively limited.

Now, modifications of the above embodiments will be described.

In the first to fourth embodiments, the nitrogen gas 35 is used as the gas, which is sealed in the space 37 of the gas chamber 32, 32A, 32B, 32C. However, the gas, which is sealed in the space 37 of the gas chamber 32, 32A, 32B, 32C, is not limited to the nitrogen gas. For example, helium gas, argon gas or air can be used as the gas sealed in the space 37 of the gas chamber 32, 32A, 32B, 32C in place of the nitrogen gas. Each of these gases has the thermal conductivity much lower than the metal material of the high pressure pump 1, 2, 3, 4 or the other solid material(s). In the case where the air is used as the gas filled in the space 37 discussed above, it is not absolutely necessary to seal the air into the space 37 of the gas chamber 32, 32A, 32B, 32C. In such a case, the space 37 may possibly be left as an open space unlike the first to fourth embodiments, in which the space 37 is formed as the closed space. For instance, the one end portion 361 of the outer blocking wall 36 may be spaced from the seal element 25 or may be engaged with the seal element 25 without entirely welding therebetween in the circumferential direction in a manner that enables the fluid communication between the space 37 and the outside space located outside of the outer blocking wall 36. Therefore, at the time of connecting and securing the inner blocking wall 33, 33A, 33B or the outer blocking wall 36 to the seal element 25, it is possible to use any other method, which is other than the welding-all-around the seal element 25.

Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader terms is therefore not limited to the specific details, representative apparatus, and illustrative examples shown and described. 

1. A high pressure pump comprising: a plunger; a pump body that includes: a cylinder hole, in which the plunger is adapted to reciprocate in an axial direction thereof; a pressurizing chamber, which is communicated with the cylinder hole and in which fuel is pressurized by reciprocating movement of the plunger; a low pressure fuel passage, which communicates between the pressurizing chamber and a fuel inlet; and a discharge passage, which communicates between the pressurizing chamber and a fuel outlet; variable volume chamber forming means for forming a variable volume chamber, a volume of which changes by the reciprocating movement of the plunger, wherein the variable volume chamber is placed adjacent to a step surface of the plunger, and the step surface of the plunger is located between a large diameter portion of the plunger, which has an end portion exposed to the pressurizing chamber and is slidable along an inner peripheral wall surface of the cylinder hole, and a small diameter portion of the plunger, which extend from the large diameter portion in the axial direction on a side opposite from the pressurizing chamber; and a gas chamber that is placed adjacent to the variable volume chamber on a side of the variable volume chamber, which is opposite from the cylinder hole.
 2. The high pressure pump according to claim 1, wherein the gas chamber includes: an inner blocking wall, which borders on the variable volume chamber and contacts fuel in the variable volume chamber; an outer blocking wall, which is opposed to the inner blocking wall; and gas, which fills a space that is defined between the inner blocking wall and the outer blocking wall.
 3. The high pressure pump according to claim 2, wherein the inner blocking wall is made of a resiliently deformable member.
 4. The high pressure pump according to claim 2, wherein: one end portion of the inner blocking wall extends in a direction generally perpendicular to a central axis of the cylinder hole; a wall surface of the one end portion of the inner blocking wall, which is located on a side where the pressurizing chamber is located, is opposed to the step surface of the plunger; a seal member is installed to surround the small diameter portion of the plunger in a circumferential direction; and an opposite wall surface of the one end portion of the inner blocking wall, which is located on an opposite side that is opposite from the pressurizing chamber, contacts an end portion of the seal member, which is located on a side where the pressurizing chamber is located.
 5. The high pressure pump according to claim 2, wherein the outer blocking wall is a seal element, which is fixed to the pump body.
 6. The high pressure pump according to claim 2, wherein the outer blocking wall is made of a heat insulation member.
 7. The high pressure pump according to claim 2, wherein the inner blocking wall is a seal element, which is fixed to the pump body.
 8. The high pressure pump according to claim 2, wherein: the inner blocking wall is welded to the outer blocking wall; and the gas is sealed in the space, which is a closed space and is defined between the inner blocking wall and the outer blocking wall.
 9. The high pressure pump according to claim 2, wherein the gas is one of nitrogen gas, helium gas, argon gas and air.
 10. The high pressure pump according to claim 2, wherein: the low pressure fuel passage includes a damper chamber, which is formed in the pump body and receives a pulsation damper that is adapted to damp pressure pulsation of fuel in the damper chamber; and the variable volume chamber is in fluid communication with the damper chamber through a return passage formed in the pump body.
 11. The high pressure pump according to claim 2, wherein: a plunger stopper is joined to the pump body on an axial side of the plunger stopper where the pressurizing chamber is located; the plunger stopper is adapted to abut against the step surface of the plunger when the plunger is moved in a direction away from a top dead center of the plunger; a seal member is installed to surround the small diameter portion of the plunger in a circumferential direction on an axial side of the plunger stopper, which is opposite from the pressurizing chamber in the axial direction; the seal member is axially clamped between the plunger stopper and one of the inner blocking wall and the outer blocking wall; and the plunger stopper includes at least one radial passage, through which a radially inner portion of the variable volume chamber located on a radially inner side of the plunger stopper is in fluid communication with a radially outer portion of the variable volume chamber located on a radially outer side of the plunger stopper. 